Second messenger pathways involved in up-regulation of an L-type calcium channel.
Second messenger pathways involved in up-regulation of an L-type calcium channel.
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第二信使途径涉及 L 型钙通道的上调。
DOI：
10.1017/s0952523800173134
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发表时间：
2000
影响因子：
1.9
通讯作者：
Linn,CL
中科院分区：
文献类型：
--
作者：
Linn,CL
鲶鱼视锥水平细胞含有一个电压门控L型钙通道，该通道通过激活代谢型谷氨酸受体（mGluRs）来调节。用mGluR I激动剂（S）-3，5-二羟基苯甘氨酸[（S）3，5-DHPG]激活I组mGluR，增强峰值钙电流幅度，移动对应于峰值电流活性的膜电位，并加宽钙电流的激活范围。在这项研究中，我们已经研究了连接激活的mGluRs与“上调”的钙电流活性的机制。在有利于L型钙电流表达的全细胞电压钳条件下，我们提供了mGluRs激活启动二酰基甘油（DG）第二信使途径激活蛋白激酶C（PKC）和上调钙通道活性的证据。这一证据是基于使用多种PKC激活剂和抑制剂的结果。PKC激活剂模拟（S）3，5-DHPG对钙电流活性的作用。如果存在PKC抑制剂，则PKC激活剂或（S）3，5-DHPG对钙通道的上调被消除。这些结果还表明，I组mGluR的激活与百日咳毒素敏感性G蛋白相关。当GTP类似物5-O-（3-硫代三磷酸鸟苷（GTPγS）扩散进入电压钳细胞时，钙通道发生上调，并模仿（S）3，5-DHPG的作用。但当百日咳毒素（PTX）与GTPγS一起沿着扩散进入细胞时，GTPγS不能调节钙电流活性。IP 3（肌醇1，4，5三磷酸）是通过激活I组mGluR产生的第二产物。一旦形成，IP 3可以触发钙从IP 3敏感的细胞内储存释放。为了确定IP 3第二信使系统是否参与钙通道的上调，将（S）3，5-DHPG施加于含有不同浓度的钙缓冲剂EGTA的电压钳位的视锥水平细胞。低浓度的EGTA不能缓冲从细胞内储存释放的钙。在低浓度EGTA存在下，（S）3，5-DHPG对钙电流幅度的增强作用降低。在细胞内钙储存阻滞剂肝素的存在下，低浓度EGTA对钙电流振幅的抑制被消除。这些结果表明，DG和IP 3的第二信使途径参与调制的电压门控钙通道在鲶鱼视锥水平细胞。DG通路上调电压门控钙通道活性，而从IP 3细胞内储存释放的钙抑制峰值电流幅度。
Catfish cone horizontal cells contain a voltage-gated L-type calcium channel that is modulated by activation of metabotropic glutamate receptors (mGluRs). Activation of group I mGluRs with the mGluR I agonist, (S)-3,5-dihydroxyphenylglycine [(S) 3,5-DHPG], potentiated peak calcium current amplitude, shifted the membrane potential corresponding to peak current activity, and widened the calcium current's activation range. In this study, we have examined the mechanisms linking activation of the mGluRs with “up-regulation” of calcium current activity. Under whole-cell voltage-clamp conditions favoring expression of the L-type calcium current, we provide evidence that activation of mGluRs initiate the diacylglyceral (DG) second messenger pathway to activate protein kinase C (PKC) and up-regulate calcium channel activity. This evidence was based on results using a number of PKC activators and inhibitors. PKC activators mimicked the effect of (S) 3,5-DHPG on calcium current activity. Up-regulation of the calcium channel by PKC activators or (S) 3,5-DHPG was eliminated if PKC inhibitors were present. These results also demonstrated that activation of group I mGluRs were linked to a pertussis toxin sensitive G-protein. When the GTP analog, guanosine 5-0-(3-thiotriphosphate (GTPγS), was allowed to diffuse into voltage-clamp cells, up-regulation of the calcium channel occurred and mimicked the effect of (S) 3,5-DHPG. However, when pertussis toxin (PTX) was allowed to diffuse into the cell along with GTPγS, GTPγS failed to modulate calcium current activity. IP3 (inositol 1,4,5 triphosphate) is a second product produced by activation of group I mGluRs. Once formed, IP3 can trigger calcium release from IP3-sensitive intracellular stores. To determine if the IP3 second messenger system was involved in up-regulation of calcium channel, (S) 3,5-DHPG was applied to voltage-clamped cone horizontal cells containing different concentrations of the calcium buffer, EGTA. Low concentrations of EGTA failed to buffer calcium released from intracellular stores. In the presence of low EGTA concentrations, (S) 3,5-DHPG's enhancement of the calcium current amplitude was reduced. Inhibition of the calcium current amplitude in low concentrations of EGTA was eliminated in the presence of the intracellular calcium store blocker, heparin. These results suggest that both the DG and IP3 second messenger pathways are involved in modulation of the voltage-gated calcium channel in catfish cone horizontal cells. The DG pathway up-regulates the voltage-gated calcium channel activity whereas calcium released from IP3 intracellular stores inhibits peak current amplitude.